Abrading apparatus with rotary index table

ABSTRACT

An abrading apparatus has a rotatably reciprocating worktable, and a vertical nozzle for directing an abrasive stream downwardly toward the worktable. The worktable has a plurality of workpiece holding zones thereon, each being designed to locate and secure a workpiece which is to be abraded. A control system is provided which includes a manual-automatic switch, the latter permitting the apparatus to be operated in either of two modes. In the manual mode, an operator depresses a switch to index the worktable to bring a holding zone, and consequently a workpiece under the abrading nozzle; the operator then depresses a second switch to initiate and complete the abrading operation. In the automatic mode, the operator depresses a single switch to index the worktable, and initiate and complete the abrading operation. In both modes, as one workpiece is being abraded, the operator is locating another in the holding zone which will subsequently be moved under the abrading nozzle.

United States Patent [391 Callahan et al.

[ Dec. 18, 1973 ABRADING APPARATUS WITH ROTARY INDEX TABLE [73] Assignee: Pennwalt Corporation, Philadelphia,

[22] Filed: Jan. 26, 1972 [21] Appl. No.: 220,977

[52] US. CL. 51/8 [51] Int. Cl. B24c 3/22 [58] Field oiSearch 51/14, 15,216 R, 51/216 ND, 216 H, 240 R, 240 T, 8

[56] References Cited UNITED STATES PATENTS 3,694,972 10/1972 Emeis 51/8 X 3,534,503 10/1970 Kulischenko r Sl/8 3,142,942 8/1964 Celovsky 51/216 ND X 2,365,152 12/1944 Stearman 51/15 3,262,234 7/1966 Roach 51/15 X 3,685,209 8/1972 Lambert 51/14 FOREIGN PATENTS OR APPLICATIONS 389,343 1/1924 Germany 51/15 Primary Examiner-Donald G. Kelly Atl0rney--Edward A. Sager 5 7 ABSTRACT An abrading apparatus has a rotatably reciprocating worktable, and a vertical nozzle for directing an abrasive stream downwardly toward the worktable. The worktable has a plurality of workpiece holding zones thereon, each being designed to locate and secure a workpiece which is to be abraded. A control system is provided which includes a manual-automatic switch, the latter permitting the apparatus to be operated in either of two modes. In the manual mode, an operator depresses a switch to index the worktable to bring a holding zone, and consequently a workpiece under the abrading nozzle; the operator then depresses a second switch to initiate and complete the abrading operation. In the automatic mode, the operator depresses a single switch to index the worktable, and initiate and complete the abrading operation. In both modes, as

one workpiece is being abraded, the operator is locating another in the holding zone which will subsequently be moved under the abrading nozzle.

10 Claims, 4 Drawing Figures PMENTED [IEC 18 I975 sum 10! 3 BACKGROUND OF THE INVENTION The present invention relates in general to abrading apparatus for carefully removing material from a workpiece such as a miniature electrical resistor. More particularly, it relates to abrading apparatus having an improved control systemwhich indexes a rotary worktable to bring a workpiece under an abrading nozzle, and then automatically initiates the abrading operation.

Miniature electrical resistors have a conductive film of electrically resistant material on a non-conductive substrate between spaced terminals. Such miniature resistors are made by first printing a slightly excessive amount offilm on the substrate, and then removing a portion of the film between the terminals so as-to reduce the cross-sectional area disposed between the terminals until the electrical resistance of the element is adjusted upwardly to the desired value.

With increasing use of abrading apparatus for mass production of miniature circuits, a need has developed for increasing the speed of the overall operation in order to increase the production of the miniature circuits.

Various means have been developed,.and are in use at the present, to quickly and accurately locate the workpiece or substrate on the worktable beneath the abrading nozzle. One such means is a clamping device which provides a three point contact for securely and accurately locating a substrate or workpiece under the abrading nozzle, the clamping device being fixed to the worktable to define a workpiece holding zone thereon. Such a device is clearly described in US. Pat. No. 3,577,682. As presently used however, there is only one of these clamping devices located beneath the abrading nozzle. Thus, each workpiece must be manually removed after the abrading operation, and another inserted in its place after which the abrading operation is once again initiated. While this clamping device allows the workpiece to be accurately located beneath the abrading nozzle, the abrading operation must be completed before another workpiece can be inserted.

Another means for rapidly and accurately locating a workpiece beneath the abrading nozzle includes having a plurality of locator pins mounted in the worktable to define a workpiece holding zone. Such pins are utilized in the invention disclosed in the instant application. Heretofore however, only a single holding zone has been so defined on the worktable. As is true with the means described in the preceding paragraph, the worktable is initially adjusted by means ofa suitable mechanism, e.g., a mechanism as described in US. Pat. No. 3,593,459, in order to locate the holding zone and consequently the workpiece, beneath the abrading nozzle. After the initial adjustment, the position of the worktable with respect to the abrading nozzle does not change throughout an abrading operation.

Neither of the above described means however, is sufficient to meet the needs of today, i.e., increased productivity. Each of these means presently in use permits the operator to quickly and accurately locate the workpiece beneath the abrading nozzle after which the abrading operation must be initiated by the operator; the operator must then remove the finished workpiece and replace it with another workpiece after which the abrading operation must once again be initiated by the operator. Thus, the operator must wait until each workpiece has been abraded before another workpiece can -be located and secured in place on the worktable; after so locating the workpiece, the operator must then activate the proper controls to initiate the abrading operation.

Consequently, what is needed, is an abrading apparatus which is capable of high speed production, one which will permit locating and securing one workpiece on the worktable while another is being simultaneously abraded.

SUMMARY OF THE INVENTION The present invention relates to abrading apparatus in general, but more particularly to abrading apparatus provided with a rotary worktable, and an improved control system for operating the apparatus.

The rotary worktable has two workpiece holding zones thereon for locating and holding the workpieces. The operator locates a first workpiece on one of the holding zones, and then actuates a control mechanism to index the worktable and bring the holding zone and workpiece beneath the abrading nozzle, after which the abrading operation automatically begins. As the abrading-operation is taking place on the first workpiece, the operator locates a second workpiece on the other holding zone on the worktable. By the time the second workpiece has been located on the worktable, the abrading operation on the first workpiece has been completed; the operator again actuates the control mechanism to index the worktable, and bring the second workpiece beneath the nozzle after which the abrading operation is once again automatically initiated; indexing the worktable also brings the first or finished workpiece to the operator, who then removes the finished workpiece, and replaces it with another workpiece which is to be abraded.

Thus, with the present invention, it is necessary for the operator to separately actuate a control mechanism to initiate the abrading operation, and then wait for this operation to be completed before locating another workpiece on the worktable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an abrading apparatus constructed and arranged for carrying out the invention.

FIG. 2 is a plan view of the rotary worktable showing two workpieces mounted in place in their respective holding zones.

FIG. 3 illustrates an electrical control system for carrying out the present invention.

FIG. 4 illustrates a pneumatic control system carrying out the present invention, this system being utilized in conjunction with the electrical control system illustrated in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, abrading apparatus 10 is shown, the latter including an abrading nozzle designated generally by the numeral 12, the nozzle including a hood 13 which surrounds the nozzle outlet (not shown). A source of vacuum is connected to the interior of hood 13 to remove the abrasive powder and other residue during the operation of the apparatus. A high velocity abrasive stream issues from nozzle 12, and is directed downwardly toward the rearwardly located workpiece l4 (miniature electrical resistor in the present example) located on rotary worktable 16.

As is more fully described in U.S. Pat. No. 3,534,503, the flow of airborne abrasive particles is initiated by the energization of a solenoid operated pinch valve in the upstream end of a supply conduit. The outlet of nozzle 12 has a restricted orifice e.g., 0.0l8 inch diameter of much smaller cross-sectional flow area than the supply conduit leading into the nozzle. As more fully described in the last mentioned patent, the supply conduit is supplied with abrasive powder by a mixing chamber where dry, filtered, pressurized air about 85 psi from a compressor is uniformly mixed in the desired proportions with abrasive powder from a reservoir.

Each workpiece 14 being an electrical resistor having a fixed electrically resistive film printed on a correspondingly shaped substrate, is trimmed by movement of nozzle 12 across the surface thereof until the electrical resistance of the resistor is adjusted upwardly to the desired value, at which time the trimming (abrading) operation is automatically terminated. Via probes 18, an electronic control and measuring system utilizing a bridge circuit measures or monotors the resistance during the trimming operation and stops the trimming when a predetermined resistance value has been reached. This operation is more fullydescribed in the last mentioned patent, and the structure comprising the probe 18 and the arcuate supporting arm on which the latter probes are mounted, are more fully described and illustrated in U.S. Pat. No. 3,551,807. Upon reaching the predetermined resistance value, probes 18 are lifted via arm 20 from the surface of workpiece 14 at the termination of the trimming operation.

During this trimming operation, the operator has mounted a second workpiece 14 on the front of the worktable 16, and upon actuation of theproper control (such as a footswitch), worktable 16 is indexed to move the latter mentioned workpiece from a loading zone around to an abrading zone under nozzle 12, and move the finished workpiece in opposite or reverse direction back to the front into the loading zone so that the operator may remove the latter and replace it with another resistor which is to be trimmed. The loading zone is outside the abrading zone.

Arm 20 is pivotally mounted within casing or cabinet 22 in order to allow the probes 18 to be lowered onto the surface of the workpiece prior to initiating the trimming operation, and raised when the trimming operation is completed. To index worktable 16 a pneumatic cylinder 24 is utilized to rotate the worktable through a suitable rack and pinon arrangement (see FIG. 4). A line 25 is connected to the rearward side of each end of cylinder 24 to alternately supply and exhaust opposite ends thereof.

worktable 16 and cylinder 24 are mounted on an X-Y slide structure designated generally by the numeral 26, the latter in turn being supported on a mounting block 27. X-Y slide structure 26 is more fully described in U.S. Pat. No. 3,593,459, but is utilized in the present embodiment to provide the initial adjustment in order to be certain that each of the workpieces 14 will be rotated to the desired location under nozzle 12 upon indexing the worktable.

worktable 16 is indexed by rotating the same in a clockwise or counterclockwise direction until member 28 (mounted beneath worktable 16) contacts stops 30 or 32, the latter being stationarily mounted on the apparatus 10. As member 28 contacts one or the other of stops 30 or 32, a button 34 (also mounted beneath I worktable 16) contacts and closes either microswitches S2 and S4, or $1 and S3, the effects of which will be more fully described below. Worktable 16 is always in one extreme position or the other, and consequently one pair or the other of the above mentioned microswitches is closed while the other pair is open.

As can be seen in FIG. 2, worktable 16 is indexed by rotatably reciprocating the same 180, alternating between clockwise or counterclockwise directions of rotation during successive movements, as indicated by the arrow 36. This serves to move a workpiece 14 to a position in the abrading zone beneath nozzle 12 after which the trimming operation is automatically initiated by means described more fully hereinafter. As one workpiece is thus moved to a position in the abrading zone beneath nozzle 12, a finished workpiece which has just been abraded is moved to the front into a loading zone so that the operator can remove the same and replace it with another workpiece which is to be abraded. As can be seen, each workpiece 14 is located against a plurality of locator pins 38 which protrude from the upper surface of work table 16. in the present embodiment, pins 38 define two workpiece holding zones or spaced apart workpiece holders, the workpieces being securely held in these zones by means of vacuum lines (not shown) which extend through the surface of the table. Such a vacuum holding means is well known in the art and forms no part of the present invention. 1

Thus, as can be seen with reference to FIGS. 1 and 2, worktable 16 is initially adjusted via X-Y slide structure 26 so that the rearwardly located workpiece is in the desired location beneath nozzle 12. After this initial adjustment, each rotation of worktable 16 will move one of the workpieces to a position beneath nozzle 12. As the workpiece in the rearward location is being trimmed, the operator locates a second workpiece against pins 38, and upon completion of the trimming or abrading operation on the rearwardly located workpiece, the operator actuates the proper control to rotate table 16 via cylinder 24 to index the table, thus moving the lattermentioned workpiece to a position beneath nozzle 12, and moving the finished workpiece to the front where it is removed by the operator, and another workpiece inserted in its place. This operation is continually repeated, thus resulting in high speed production.

Referrring to FIGS. 3 and 4, the means for operating apparatus 10 in the above described manner will be dis cussed in more detail. As stated above, because worktable 16 is always in one extreme position or the other, one of the pairs of microswitches 81-83 or 82-84 will be closed depending upon the position of the worktable. To explain the operation of the system, it will be assumed'that microswitches 31-83 are closed (shown open in FIG. 3), that microswitches 82-84 are open, that probes 18 are down, i.e., in contact with the resistor whichis to be trimmed, and that RL 1 is energized. RL 1 being energized, its normally open contacts E-F and G-H will now be closed; the G-H contacts are latching contacts for holding in the RL 1 relay.

lf switch 814R is now closed (shown open in FIG. 3) RL 2 is energized thus closing its normally open contacts C-D and l-J, and opening its normally closed contacts A-B. Switch S5 now closes, energizing solenoid 44 through RL 2 contacts 1-]. As a result, worktable l6 indexes, opening microswitches 81-83. The entire electrical circuit is de-e nergized during the indexing period because during the brief time that worktable 16 is rotating, microswitches Sit-S3 and 52-84 are all open as shown in FIG. 3. Dotted lines 39 and 41 indicate that these microswitches operate in pairs.

At the conclusion of the indexing operation. microswitches S2S4 close (see FIG. 2 also), re-energizing probe lift solenoid 4t) and consequently lowering probes 18. Only when probes 18 are lifted from the surface of a resistor 14 can worktable 16 rotate. As a result of probe lift solenoid 44 being re-energized, RL 1 is again energized thus resetting the system.

The trimming or abrading operation may be initiated either manually or automatically. It is initiated manually by depressing either footswitch S14L, or pushbutton S11. Switch S7 is shown in the manual position.

For automatic initiation of the trimming operation, S7 is moved (closed) to the automatic position. Fluidic switch S 12 will now close automatically after the worktable has indexed, and probes 18 are lowered onto the surface of resistor 14, to initiate the trimming operation automatically. This will be described in more detail below. After switch S 12 is closed however, the trimming operation begins. The resistor trimming bridge controls the trimming operation by measuring the resistance of resistor 14 during trimming, and when a predetermined resistance valve is reached, a signal is transmitted to the pinch triac (which includes the pinch valve referred to above) to terminate the trimming or abrading operation. A more thorough explanation of the control system utilized for controlling the abrading operation is set forth in the above mentioned US. Pat. No. 3,534,503.

The pneumatic system for carrying out the present invention is illustrated in FIG. 4.

Air enters line 46, passes through regulator R1, and then through three-way valve Vl (if open) to probe lift cylinder 47. It is noted that probes 18 and arm 20 are normally biased downwardly by a spring 50 which contacts piston 49. In order to raise probes l8 and permit indexing of worktable 16, air must be supplied to cylinder 47 to raise piston 49.

A portion of the air entering line 46 is directed through a second pressure regulator R2, through a re der 47 as indicated by dotted line 52. Consequently, as

probes 18 are lowered onto the surface of a resistor 14, the air discharge from nozzle 54 is restricted, raising the pressure in bellows 61 and closing switch S12 (see FIG. 3 also) to automatically initiate the trimming or abrading operation. As stated above, this assumes that switch S7 is in the automatic position. Thus, by merely actuating a single switch 814R, the operator indexes worktable 16 and initiates the trimming operation. If switch S7 is in the manual position, either switch S14L or S11 must be actuated to initiate the trimming operation, after actuating 514R to index the worktable. If switch S7 is placed in the automatic po- 6 sition prior to beginning a production run, the operator need only actuate the single switch 814R thereafter to index the table and trim each workpiece or resistor.

To index worktable 16, air is directed through line 60, through a four-way valve V2, and to one end or the other cylinder 24 via lines 62 and 64. One end of the latter cylinder is supplied with air, while the other is exhausted. Valve V2 is an either-or type valve meaning that the valve stays in the last position to which it was moved until receiving a signal through one of the solenoids 42 or 44 (see FIG. 3 also). Worktable 16 is rotated, first l in one rotational direction and then in opposite rotational direction, by means of rack 66. The rack 66 is reciprocated by the force of the pressure differential on its pistons and drives pinions 68, the latter being connected to the worktable by a shaft 69 (see FIG. 2 also).'Thus, worktable 16 stays in one or the other of its extreme positions until. valve V2 is shifted once again via one of the solenoids 42 or 44. With this arrangement, the indexing means rotatably reciprocates the worktable 16 to move the workpiece holders alternately first in one direction to position one of the holders in the abrading zone and the other holder in the loading zone, and then in reverse or opposite direction in. order to position the holder which had been in the abrading zone in the loading zone and to position the holder which had been in the loading zone in the abrading zone.

It is also noted that S5 (see FIG. 3) is mechanically linked to probe lift cylinder 47, so that upon lifting probes 18, switch S5 will be shifted to the position opposite that illustrated in FIG. 3 so that worktable 16 can be indexed. As stated above, the worktable l6 cannot be indexed as long as probes 18 are contacting a resistor or workpiece 14.

Although it is not essential, in the preferred embodiment, switches 814R and S14L are contained in a single primary footswitch, 514R being the right pedal, and SML being the left pedal thereof. Each of these switches is illustrated in its normal position in FIG. 3, i.e., when neither pedal of the primary footswitch has been depressed by the operator.

We claim:

1. Abrading apparatus comprising a. a nozzle for directing a stream of abrading material to an abrading zone;

b. means for supplying a pressurized stream of abrading material to said nozzle;

c. a worktable having first and second holders spaced apart thereon, each holder being adapted to hold a workpiece, said worktable being rotatable in a generally horizontal plane to position one of said holders at a time in said abrading zone and simultaneously to position the other of said holders in a loading zone outside said abrading zone;

d. indexing means for rotatably reciprocating said worktable to move said holders alternately first in one direction to position said first and second holders in the abrading and loading zones respectively, and then opposite to said one direction to position said first and second holders in the loading and abrading zones respectively; and

e. means for initiating the flow of said abrasive stream from said nozzle toward a workpiece supported on the one of said holders positioned in said abrading zone.

2. Abrading apparatus according to claim 1, and further including means having a plurality of probes engageable with a workpiece in said abrading zone for monitoring a characteristic of said workpiece and terminating the flow of said abrasive stream when a predetermined value of said characteristic has been reached.

3. Abrading apparatus according to claim 2, and further including means for preventing the indexing of said worktable while said probes are contacting said workpiece.

4. Abrading apparatus according to claim 1, wherein said worktable is mounted for rotation about a vertical axis.

5. Abrading apparatus according to claim 4, wherein said indexing means includes abutment means for stopping the rotation of said worktable at selected positions.

6. Abrading apparatus according to claim 5, wherein the means for indexing said worktable includes switch means, and means connected to said worktable for contacting said switch means at said seiected positions.

7. Abrading apparatus according to claim 6, and further including slide means for adjusting the position of said worktable with respect to said abrading nozzle, said worktable being mounted to said slide means and adapted to slide in a plurality of directions which are perpendicular to each other.

8. Abrading apparatus according to claim 7. wherein said indexing means includes a rack and pinion arrangement, said pinion being in driving relation to said worktable, a rack geared in driving relation to said pinion, and a reciprocating pneumatic cylinder in driving relationship with said rack.

9. Abrading apparatus according to claim 5 wherein the selected positions are approximately apart about said axis.

10. Abrading apparatus according to claim I selectively operable in manual and automatic modes having electrical circuitryassociated with said indexing means and said initiating means including: a first switch for actuating said indexing means and said initiating means for automatic mode operation, and a second switch for actuating said initiating means independently of said first switch for manual mode operation. 

1. Abrading apparatus comprising a. a nozzle for directing a stream of abrading material to an abrading zone; b. means for supplying a pressurized stream of abrading material to said nozzle; c. a worktable having first and second holders spaced apart thereon, each holder being adapted to hold a workpiece, said worktable being rotatable in a generally horizontal plane to position one of said holders at a time in said abrading zone and simultaneously to position the other of said holders in a loading zone outside said abrading zone; d. indexing means for rotatably reciprocating said worktable to move said holders alternately first in one direction to position said first and second holders in the abrading and loading zones respectively, and then opposite to said one direction to position said first and second holders in the loading and abrading zones respectively; and e. means for initiating the flow of said abrasive stream from said nozzle toward a workpiece supported on the one of said holders positioned in said abrading zone.
 2. Abrading apparatus according to claim 1, and further including means having a plurality of probes engageable with a workpiece in said abrading zone for monitoring a characteristic of said workpiece and terminating the flow of said abrasive stream when a predetermined value of said characteristic has been reached.
 3. Abrading apparatus according to claim 2, and further including means for preventing the indexing of said worktable while said probes are contacting said workpiece.
 4. Abrading apparatus according to claim 1, wherein said worktable is mounted for rotation about a vertical axis.
 5. Abrading apparatus according to claim 4, wherein said indexing means includes abutment means for stopping the rotation of said worktable at selected positions.
 6. Abrading apparatus according to claim 5, wherein the means for indexing said worktable includes switch means, and means connected to said worktable for contacting said switch means at said selected positions.
 7. Abrading apparatus according to claim 6, and further including slide means for adjusting the position of said worktable with respect to said abrading nozzle, said worktable being mounted to said slide means and adapted to slide in a plurality of directions which are perpendicular to each other.
 8. Abrading apparatus according to claim 7, wherein said indexing means includes a rack and pinion arrangement, said pinion being in driving relation to said worktable, a rack geared in driving relation to said pinion, and a reciprocating pneumatic cylinder in driving relationship with said rack.
 9. Abrading apparatus according to claim 5 wherein the selected positions are approximately 180* apart about said axis.
 10. Abrading apparatus according to claim 1 selectively operable in manual and automatic modes having electrical circuitry associated with said indexing means and said initiating means including: a first switch for actuating said indexiNg means and said initiating means for automatic mode operation, and a second switch for actuating said initiating means independently of said first switch for manual mode operation. 